The invention relates to a disc brake of hydraulic self-energizing design with a readjustment device.
A disc brake with an electromotive actuator of self-energizing design and with a brake-internal hydraulic arrangement is described in the applicant's application WO 2007/045430 A1.
A readjustment device of a disc brake of the type is composed of a relatively large number of parts.
It is the object of the present invention to improve a readjustment device of a generic disc brake.
It is thereby possible to realize a wear-compensating readjustment which permits the construction of a compact disc brake with a smaller number of parts than in the prior art.
According to the invention, the disc brake is provided with a readjustment device for readjustment to compensate brake pad wear, wherein the readjustment device has an adjustable screw spindle which serves, in operative connection with the brake-application device, for generating a follow-up movement of the at least one brake pad. Here, the screw spindle is integrated in a particularly space-saving manner into the at least one brake-application cylinder. The screw spindle can furthermore be coupled to the electromotive actuator in order to be driven, and has a readjustment piston which can be hydraulically adjusted in the tangential force absorption cylinder during a follow-up movement of the at least one brake pad.
Functional reliability of wedge angle switching and pressure boosting is thus also permitted in a simple manner.
A disc brake of self-energizing construction comprises the following: a brake-internal hydraulic arrangement with a reservoir circuit and an expansion vessel; a brake-application device having at least one brake-application cylinder for the brake-application movement of at least one brake pad in the direction of a brake disc; at least one force transmission unit which supports the at least one brake pad on the brake-application device at a wedge angle; at least one tangential force absorption cylinder for wedge angle switching, which tangential force absorption cylinder is operatively connected to the at least one force transmission unit; an electromotive actuator which acts on the brake-application device via the hydraulic arrangement; a distributor cylinder for pressure boosting, which distributor cylinder is arranged in series between the electromotive actuator and the brake-application device; and a control unit which is provided for controlling the wedge angle switching between the tangential force absorption cylinder and the electromotive actuator, wherein the disc brake comprises a readjustment device for readjustment to compensate brake pad wear, wherein the readjustment device has an adjustable screw spindle, which is operatively connected to the brake-application device for the purpose of generating a follow-up movement of the at least one brake pad and can be coupled to the electromotive actuator in order to be driven, and a readjustment piston, which can be hydraulically adjusted in the tangential force absorption cylinder during a follow-up movement of the at least one brake pad.
It is thus possible, likewise in a space-saving manner, for a readjustment drive wheel with a shaft drive wheel coupled to the screw spindle to be designed as a hydraulic gear motor, which can be hydraulically coupled to the electromotive actuator by way of a hydraulic switch. The hydraulic switch can preferably be controlled by the control unit.
A great advantage is that the drive of the readjustment device is realized hydraulically. The gear motor can be of flat construction, and the hydraulic lines can be integrated into the housing.
It can also be made possible in this way for the readjustment piston to be connectable, for a follow-up movement, to the reservoir circuit by way of a directional valve.
In a preferred embodiment, it is provided that the expansion vessel of the reservoir circuit of the brake-internal hydraulic arrangement is equipped with a sensor for detecting pad wear, wherein the sensor is connected to a brake control unit which, for the activation of the readjustment device for a corresponding follow-up movement of the at least one brake pad, is coupled at least to the electromotive actuator and to the control unit. A brake control unit of this type is provided in a brake of this type in any case, and can be upgraded with corresponding software in a simple manner. An auxiliary unit may self-evidently also be provided. The sensor for the liquid level in the expansion vessel may thus be used as a travel sensor for measurement of the horizontal adjustment of the brake pads, detection of hydraulic fluid losses, and determination of the brake pad wear status. Instead of a travel sensor, use may also be made, as an inexpensive alternative, of a pressure sensor to detect the present oil quantity in the expansion vessel.
In a preferred embodiment, the control unit may have a control disc which can be driven hydraulically, by way of a control drive in the form of a hydraulic gear motor, by the electromotive actuator via a switching valve. It is possible in this way, by way of simple control means, for the electromotive actuator to be used as a drive for different tasks. In this case, the electromotive actuator, in addition to its function as a pressure generator for the brake-application device, acts as a drive source for the readjustment device and the control device.
The readjustment device may be provided with an emergency release device, which is preferably coupled to the readjustment drive wheel. In this way, not only is a manual release of the brake possible in the event of an emergency, but a resetting of the brake-application device is also possible for example in the event of a pad change.
The follow-up movement of the brake pads in the event of wear may take place after a certain number of braking operations. In the simplest case, the readjustment takes place at the end of every actuation of the parking brake, because here, the air play between the mechanical abutment of the screw spindle wheel against the cylinder base and the contact point of the brake pads with the disc must be newly set in any case.
In normal, unbraked driving operation for an intelligent follow-up movement in the event of wear of the brake pads (and also of the brake disc), it is alternatively possible for the readjustment device to be equipped with at least one sensor. The sensor may detect a readjustment travel in order to determine a present follow-up movement, and transmit the readjustment travel to the brake control unit for the regulation of the readjustment device. The brake control unit can, in a conventional manner, compare the present travel with a comparison value stored for example in a table, and thus always set the brake pad with its required air play.
For this purpose, the sensor for determining a readjustment travel may be a multi-turn potentiometer which is directly or indirectly coupled to the screw spindle. Such angle sensors are available in a variety of embodiments for numerous purposes and in high quality, even for high temperatures such as may arise in a brake.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.